The first line of input contains an integer N (3 ≤ N ≤ 250 000), the number of islands. The following N lines
contain the locations of the islands. Each location is a pair of integers between 1 and 2500 (inclusive), the row and column numbers, respectively.
第一行包含一个数N,表示帆船的个数。
接下来的N行,每行包含一对数(x,y),表示帆船的位置